Account - Dan Murphy's Search
Pulled data for a campaign with the filter "Campaign Name Equals".
Dimensions used - Campaign, Ad group, data
ERROR - did now download data for one specific Ad Group = "Vegan Wine"
*Note - There was also another ad group named "Vegan Friendly Wine", for which data was being pulled.
If I understand properly, you are using the "equals" filter with the "Campaign Name" dimension. Please be sure the value you want to filter, is properly spelled. Moreover, check that you set the limit rows to "All rows" (if not, your output may be incomplete).
However, it would be useful if you share with us a screenshot or if you use the "Report an issue with a query" tool, so that we can know the exact parameters you have used (I attach an image).